During a machining process, the subject workpiece must be affixed proximal to the machine tool to ensure that the workpiece remains in a desired position when acted on by the machine tool. Typically, workpieces are affixed to a worktable that is part of the machine tool itself.
Various types of apparatus for affixing such workpieces have been proposed and constructed in the past. One common method for securing workpieces to a worktable includes the use of T-head bolts that are used in conjunction with T-shaped grooves located within the worktable.
With this method, a worktable typically has inverted T-shaped grooves beneath the worktable surface that accept an insertion therein of an inverted T-shaped head of a T-head bolt. The threaded shaft of the bolt protrudes from the surface of the worktable from within the groove to accept the placement thereon of a threaded nut.
When the nut is threaded onto the shaft of the bolt, it is tightened against the worktable surface, causing the T-shaped head of the bolt to become secured within the T-shaped groove of the table. Thus, a workpiece can be affixed directly to the table by placing it between the worktable surface and the nut of the T-head bolt and drawing the nut tight against the workpiece itself.
Furthermore, a workpiece can be indirectly fastened to a worktable using T-head bolts by placing one of a variety of clamps between the nut and worktable surface, the workpiece in turn secured within the clamp. A common embodiment of such a clamp is comprised of a fixed jaw that cooperates with a separate jaw moving under the influence of a threaded screw.
Use of a workpiece clamp allows the operator to change a given workpiece by removing the workpiece from the clamp itself while allowing the clamp to remain secured to the worktable via the T-head bolts.
However, several disadvantages exist with the aforementioned methods for securing workpieces. Use of T-head bolts to directly secure a workpiece to a worktable is often cumbersome and imprecise. One must loosen or remove one or more nuts of one or more T-head bolt when changing workpieces to be machined.
Albeit, when changing workpieces, an operator can avoid the cumbersome adjustment of T-head bolts by utilizing a clamp to secure the workpiece to the worktable, many prior art clamps limit the operator to securing only one workpiece to the table at a time.
Furthermore, modern computer-numerically-controlled (CNC) machine tools involve complex "set-up" work that requires a precise placement of the workpiece onto a worktable. This placement thereafter enables the operator to enter the exact positional coordinates of the workpiece into the machine's computer program.
Because such set-up work is time consuming, CNC machine operators desire that it not be repeated when replacing identical workpieces to be machined. The aforementioned methods of securing workpieces often require an operator to perform repeated set-up work when replacing workpieces one-after-another.
To avoid the repeated set-up work required of workpiece replacement, "pallets" have been developed to secure a plurality of workpieces to a worktable during a machining process. A typical pallet is made to hold a plurality of workpieces of a given dimension. One embodiment of such a pallet is comprised of a plate having a grid of bores or apertures therethrough, with each bore adapted to accept the precise insertion of a workpiece therein.
The workpieces may be secured to the pallet using a number of different methods, depending on the type of machining process to be performed on the workpieces. Where the machining forces exerted on the workpieces are light, the workpiece can be secured to the pallet by merely using the frictional forces present with a simple insertion of the workpiece end into the pallet bore. Heavier machining processes, by contrast, may require that the workpieces be threadedly inserted into the bores.
The pallet holding a plurality of workpieces may be secured to a worktable using the aforementioned T-head bolts. Once the pallet holding a plurality of workpieces is secured to the machine, the operator programs the location of each workpiece into the computer program of the CNC machine. The machine then performs the requisite machining process on each workpiece held in the pallet.
When the machining process is completed on each workpiece and the operator wants to replace the machined workpiece with identical feed-stock, the operator can merely replace each workpiece on the pallet while the pallet remains affixed to the worktable. Such replacement thus eliminates costly set-up time because it allows the operator to utilize the previously loaded location data within the CNC program of the previously machined workpieces.
Although pallets have helped computer-aided machine operators reduce the set-up time required for a given machining process, several disadvantages continue to exist with prior art pallets. One disadvantage present in the prior art is that a given pallet is "custom-made" to hold a plurality of workpieces of only a given dimension.
For example, a pallet made to hold a plurality of workpieces, each having a 1/4" outside diameter, cannot hold a plurality of 1/2" diameter workpieces. Because a typical prior-art pallet is not adjustable to accept a variety of workpiece sizes, a machine operator must have a separate pallet for every size of workpiece to be machined.
Another disadvantage present in prior art pallets exists with regard to how the pallet secures the plurality of workpieces therein. Some pallets require a force fit or threaded connection between each individual workpiece and the pallet. The process of securing each individual workpiece to the pallet in such pallets is undesirably time-consuming.
Other pallets, though not requiring an operator to individually secure each workpiece to the pallet, "sandwich" a series of workpieces between opposing "clamping bars," thereby securing them to the pallet. However, because the methods used to exert the opposing forces on the clamping bars are imprecise, the pallet may subject the workpieces to undue forces in the clamping process, thus risking unintentional deformation of the workpieces.